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6 Posts
Discussion Starter #1
My last batch of handloads was

- LC 18 brass (new, unfired), 1.750" trim length, 2.250" COAL
- Sierra 77g MK (with cannelure)
- RCBS 223 SB die w/polished expander ball
- Forster BR seater die
- Lee FCD (light crimp)
- CCI 41 primer
- 8208 XBR (23.6 gr to 23.9 gr, H20 capacity is about 30.2 gr with QuickLOAD and Magnetospeed V3 agreeing within 10 fps)

With the Sinclair concentricity gauge I found neck TIR to be anywhere from .001" to 0.003" before firing. Bullet TIR was anywhere from 0.002" to 0.005" measured at the start of the o-give near the case mouth. After firing most necks were showing .001" to 0.002" TIR with a few close to .003". This put me on the road of figuring out what was causing the TIR variance. I found that if I resized without the expander ball and then made another pass with just the expander ball working the brass my cases were very consistent at .001" to .0015" TIR. Keeping the expander ball in during the resizing pass showed the same variance I saw before. All necks were lubed with the Redding dry lube btw. Bullet TIR definitely improved on the cases had the mouth expanded in a separate pass.

So in an effort to refine things I ended up ordering a .2230" mandrel and die body from 21st Century. I'm finding that resizing without the expander ball then using the 21st Century expander mandrel is yield neck TIR of .001" or less consistently. Bullet TIR is consistently falling in the 0.001 to 0.0015" range.

The only other thing I might try is switching to a Redding bushing die followed by the expander mandrel. I can eliminate about .005" of neck down (vs the RCBS die) here.


862 Posts
I use both from 21st Century and Bronwells. Great way to pursue for the consistency.

6 Posts
Discussion Starter #3 (Edited)
I made it it out to the range today to test the new loads using the 21st Century mandrel. The details are as follows...

Rifle: LWRC M6A3 (16.1")
Scope: ACOG TA31F (4x)
Rest: Lead Sled Solo
Distance: 200 m

Temp: 85F
Humidity: 44%
Pressure: 30.05 inHg
Wind: 3 MPH

Brass: LC 18 (once fired, flash hole deburred, primer pocket uniformed)
Wall Thickness: ~ 0.011"
Resize: RCBS SB with 0.003" shoulder bump, expander ball removed
Neck: 21st Century Expander (0.223")
Trim Length: 1.750"
H20 Weight (after 1st firing): 31.3 gr

Bullet: Sierra MK 77 gr w/cannelure
Lee FCD Crimp: Light
Primer: CCI 41
Powder: IMR 8208 XBR @ 23.6, 23.7, 23.8, and 23.9 gr
CBTO: 1.850"
COAL: ~2.250"
Bullet Runout: Most < 0.001" with a few < 0.0015"
Bullet Jump: 0.024"

For those of you that subscribe to OBT theory my OBT is 0.887 ms. QuickLOAD indicated that the closest charge to that OBT would be 23.8 gr (0.886 ms). It turned out that 23.8 gr was in fact my best group. I believe I could tighten this up with a better scope but for what it is I'm very happy. It has no problem hitting the steel at 200 m. QuickLOAD estimates all of these loads are under NATO max pressure (with 3% powder tolerance) and in fact I saw zero signs of over pressure. The 21st Century mandrel was definitely worth it for me.

Predicted Velocity (QL): 2631 fps
Actual Velocity (Magnetospeed V3): 2612 fps / SD 13.5 / ES 36

Group Size: 2.18" (0.95 MOA)


6 Posts
Discussion Starter #4 (Edited)
Below are some things I've observed correlating QuickLOAD with Magnetospeed data. These should not be taken as gospel but I think could help those that pay attention to the finer details.

1. Bullet lot variance is significant in terms of MV in both QuickLoad and measured. I am using SMK 77 gr and have two different lots. From a weight perspective they are similar and in the 77.0-77.1 gr arena. The important differences are the average base to o-give measurements and diameter/length of boat tail taper. These measurements are key in predicting measured results accurately. For an AR15 using magazines I would put much more into keeping the seating depth consistent than worrying about bullet jump distance. If you use QL I would force the seating depth figure and let is adjust the COAL to whatever it calculates. I've found that for a given lot the base to o-give measurement is very consistent (+/- 0.001"). Bullet length is all over the place so trying to keep a consistent COAL is going to net varying velocities.

2. New vs once fired brass of the same lot... my data shows that for my LC 18 brass there is about a 0.3 gr effective delta in H2O weight as it pertains to QL and measured results. I say effective delta because the measured volume of a new prepped case is about a grain less but obviously it is able to expand to the chamber volume. Mixing new and once fired resized brass will likely net a meaningful velocity variance if you use the same charge weight. For plinking it won't matter but if you are chasing groups it will.

3. When you are at the hot end of the spectrum a case volume variance of a couple tenths of a grain can make or break peak chamber pressure estimates. Loading up random brass to a given charge approaching 5.56 limits is not wise.

4. QL powder burn rate for a given lot should be tweaked to correlate to measured results assuming all of the other parameters are as accurate a possible. This will allow for greater confidence in results as you change other parameters such as brass, bullet lot, seating depths, etc. down the road. I ended up buying an 8 lb canister of XBR just to avoid a potential performance change anytime soon.

5. Barrel time is not necessarily constant for a given MV. If you subscribe to the OBT model you need to look at the actual barrel time in QL for a given load even if it shares the same predicted MV as another load.

6. Suppressor impacts... this is my next area of interest. My grouping was relatively good and consistent with my first lot of bullets and WCC 10/12 brass but on my last suppressed outing things were a mess with the new bullet lot and LC brass. I don't know if it was due to thermals/fouling or if the barrel harmonics with the suppressor change enough that I need find the optimum charge weight when suppressed. Bullet runout could also have played a part here as I was using the expander ball rather than the mandrel (clearly works well) on new brass.

Comments/debate is welcome. I know some have far more experience than I do but if any of this helps someone else out then great.

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